In some air-conditioning apparatuses such as a multi-air-conditioning apparatus intended for an office building, a heat source unit (an outdoor unit) is provided on the outside of a building, and indoor units are provided on the inside of the building. In such an air-conditioning apparatus, a refrigerant that circulates through a refrigerant circuit transfers its heat to (or receive heat from) air that is supplied to a heat exchanger included in each of the indoor units, whereby the air is heated or cooled. Furthermore, the heated or cooled air is sent into an air-conditioned space, whereby the air-conditioned space is heated or cooled.
In many cases, a HFC (hydrofluorocarbon)-based refrigerant, for example, is employed as the heat-source-side refrigerant to be used in the above air-conditioning apparatus. In some other proposals, a natural refrigerant such as carbon dioxide (CO2) is employed as the heat-source-side refrigerant.
Other types of air-conditioning apparatuses called chillers have also been proposed in each of which a heat source unit provided on the outside of a building generates cooling energy or heating energy (see Patent Literature 1, for example). In the technology disclosed by Patent Literature 1, water, antifreeze, or the like is heated or cooled by a heat exchanger provided in an outdoor unit and is then transported to indoor units such as fan coil units or panel heaters, whereby heating or cooling is performed.
Another air-conditioning apparatus called heat-recovery chiller has been proposed in which a heat source unit and each of indoor units are connected to each other by four water pipes (see Patent Literature 2, for example). In the technology disclosed by Patent Literature 2, heated or cooled water or the like is simultaneously supplied to the indoor units, so that cooling or heating is freely selectable on the indoor units.
Yet another air-conditioning apparatus has been proposed in which a heat exchanger that exchanges heat between a primary refrigerant and a secondary refrigerant is provided near each of indoor units (see Patent Literature 3, for example).
Yet another air-conditioning apparatus has been proposed in which a heat-source-side refrigerant that has been heated or cooled by an outdoor unit is supplied to heat exchangers provided in branch units, and heating energy or cooling energy of the heat-source-side refrigerant is transferred to a heat medium via the heat exchangers (see Patent Literature 4, for example). In the technology disclosed by Patent Literature 4, the outdoor unit and each of the branch units are connected to each other by two pipes.
Yet another air-conditioning apparatus such as a multi-air-conditioning apparatus intended for an office building has been proposed in which a refrigerant is made to circulate between an outdoor unit and a relay unit while a heat medium such as water is made to circulate between the relay unit and each of indoor units, whereby the power for transporting the heat medium is reduced while the heat medium such as water is made to flow through the indoor units (see Patent Literature 5, for example).